There is stunning news out of Boston the FBI releasing surveillance tapes. Two people called persons of interest in the marathon day bombings. The FBI considers them armed dangerous asked that no one approached them but they -- ask all members of the public. To look at these tapes to study them in detail. And help. ABC's chief investigative correspondent Brian Ross is now going to take us frame by frame through these -- Brian. Well good evening Diane federal authorities now believe that a team of at least two men but responsible for the bombings there. As you say described as armed and extremely dangerous. The FBI is basing its two -- theory on these surveillance camera videos and still pictures made public late today. Two white men in their twenties according to the FBI. One with a black cap. The second with a white cap worn backwards. Both wearing backpacks at the FBI believes held the bombs off to the side of this video runners can be seen heading to the finish line. And time code markers indicate the footage was made about thirteen minutes before the first bomb went off. The FBI says only one of the two potential suspects the one with the white cap was actually seen placing his backpack at the scene of an explosion. We are releasing photos of these two suspects they are identified a suspect one and suspect to. They appear to be associated. Officials say that made the image is public now because they need help -- matching the faces to names but they warned. These are dangerous man we consider them to be it armed and extremely dangerous. They were also new developments today based on the some 300 pieces of evidence recovered from the crime scene. Some of the components including this battery and this circuit board were recognized by hobbyists as parts of its toll remote control cars. Similar to this one scene in an online video. The owner of one hobby store outside Boston says FBI agents interviewed him last night and left little doubt that -- remote control unit had been used in the bombs. I said look like to me that one of the components was a radio receiver. There's did the response was back on his -- There are instructions on the Internet about how to use a remote control toy car to set off a bomb both on the anarchist cookbook and several jihadist sites as well. There is still no indication of whether this was an act of foreign or domestic terrorism. But the president vowed today the bombers whoever they are will not escape. Yes we will find you. And yes you face justice. What happens next is what one official called an electronic dragnet. Pushing these images far and wide to engage the public in the hunt -- our Brian thank you.

This transcript has been automatically generated and may not be 100% accurate.

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